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Adverse health effects of ambient air pollution are well recognised and include increased morbidity and mortality in respiratory and cardiovascular diseases. Diesel engines are major contributors to ambient particulate matter pollution and diesel particles have been shown to have strong toxicological and oxidative properties.

Mechanistic aspects of diesel engine exhaust exposure have been investigated in bronchial mucosal biopsies sampled during bronchoscopy of human subjects exposed in a validated experimental exposure set-up. Two exposure series were performed. Two separate groups of 15 healthy subjects each were exposed to filtered air and diesel exhaust during 1 hour in random order. The first exposure series was performed with the engine at idling with a PM₁₀ concentration of 300µg/m³ and the second was carried out during urban cycle (European Transient Cycle) running conditions with 270 µg particles/m³. Bronchoscopies with sampling of bronchial mucosal biopsies were performed 6 hours after exposure. Biopsies fixed in acetone were bedded in glycolmethacrylate (GMA) resin and were stained for immunohistochemistry. Readings were done with light microscopy as well as image analyser with digital stainings processing of.

Diesel exhaust enhanced the expression of the cytokines IL-8 and GRO-α in the bronchial epithelium suggesting that the epithelium plays a major role in mediating the neutrophil-dominated airway mucosal inflammation. The bronchial expression of Th₁ and Th₂ cytokines was evaluated, addressing the hypothesis that diesel exhaust would induce a Th₂ airway response. Diesel exhaust enhanced the expression of Th₂ related cytokine IL-13 whereas the expression of Th₁ cytokines was unaffected.

The investigation of epithelial signal transduction pathways, by means of newly developed and validated cytoplasmic and nuclear stainings for key transcription factors and kinases, demonstrated that exposure to diesel exhaust increased the nuclear translocation of redox sensitive signal transduction components including phosphorylated (p)-p38-MAPK, p-JNK, p-c-jun (AP-1) and p65 (NFκB). These findings indicate novel mechanistic aspects to be involved in the airway response to particulate air pollution.

The expression of epidermal growth factor receptor (EGFR) as well as phosphorylated C-terminal Tyr 1173 increased significantly following DE exposure. The findings are consistent with the upregulation of p38 and JNK MAPkinases as well as increased NFκB expression. The MEK-ERK pathway was not affected and Src related phosphorylation was absent.

Diesel exposure at urban European transient cycle running conditions resulted in upregulation of the vascular adhesion molecule expression in the bronchial mucosa as signs of an early inflammatory response, while infiltration of inflammatory cells had not yet occurred. Differences in organic composition and particle concentration in the exhaust compared to idling situation may have influenced the outcome.

This thesis has added a mechanistic basis for the diesel exhaust induced airway inflammation in-vivo in humans. It is concluded that activation of epithelial signal transduction pathways, cytokine production and increased endothelial adhesion molecule expression play important roles in the airway inflammatory response to diesel exhaust.

Background:

In study II, the subjects were exposed for 1 hour to DE generated during idling with bronchoscopy at 6 hours. The bronchial mucosal biopsies showed significant increases in neutrophils, mast cells and lymphocytes together with bronchial wash neutrophils. Additionally, DE exposure significantly increased the nuclear translocation of the aryl hydrocarbon receptor (AhR) and phosphorylated c-jun in the bronchial epithelium. In contrast, the phase II enzyme NAD(P)H-quinone oxidoreductase 1 (NQO1) decreased after DE.

In study III, the 2-hour exposures took place in a road tunnel with bronchoscopy 14 hours later. The road tunnel exposure significantly increased the total numbers of lymphocytes and alveolar macrophages in BAL, whereas NK cell and CD56+/T cell numbers significantly decreased. Additionally, the nuclear expression of phosphorylated c-jun in the bronchial epithelium was significantly increased after road tunnel exposure.

In study IV, the subjects were exposed to metal-rich particulate aerosol for 2 hours at a subway station with bronchial biopsy and BAL sampling at 14 hours. The subway exposure significantly increased the concentration of glutathione disulphide (GSSG) in BAL, with no airway inflammatory responses. In contrast, the number of neutrophils in the bronchial mucosa and the nuclear expression of phosphorylated c-jun in the bronchial epithelium tended to decrease after the subway exposure.

In study V, the exposure to biomass smoke lasted 3 hours. Bronchoscopy was conducted 24 hours post exposure. The investigated biomass combustion emissions resulted in a significant increase in total glutathione and reduced glutathione in BAL, without any evident acute airway inflammatory responses.

Conclusion: